Screw driver with offset wings



19, 1958 a. A; SMITH ETAL 2,848,024

SCREW DRIVER WITH OFFSET WINGS Filed April is, 1958 INVENTORS BY I vUitd States Patent scREw onrvnn WITH OFFSET WINGS Ian A. Smith,Willimantic, and Herman G. Muenchinger, Chaplin, Conn.

Application April 18, 1958, Serial No. 729,488

8 Claims. (Cl. 145-50) This application is a continuation-in-part of ourapplication Serial No. 558,663, filed January 12, 1956, now abandoned.

This invention relates to driving tools for threaded fasteners, moreparticularly of the recessed head type.

Threaded fasteners having recessed or socketed heads, as distinguishedfrom slotted heads, have come into widespread use in recent years, duein large part to the dedevelopment of the so-called Phillips recess, andthe proven superiority of recessed head screws and other fasteners,particularly in manufacturing and assembly operations involving largequantities of such fasteners and likewise involving the use of powerdrivers. This trend has resulted in the provision of fasteners havingimproved torque capacity over slotted screws and the like, whichfasteners may be driven much more quickly and efficiently, and with muchless hazard to the work into which they are driven. However, the demandfor still greater torque capacity (ability to be more securelytightened, i. e. driven home with greater force), continues to be felt,and thus the search for an improved tool recess continues.

The recess of the Phillips type cannot be increased in size orpenetration beyond a certain proportion with respect to the size of thefastener, because of the relative proportions of the recess itself. Thatis, when the overall size of the recess is increased beyond a certainextent, the central portion of the recess penetrates below the depth ofthe fastener head and into the shank, thus undesirably weakening thescrew at an already critical point, namely, the junction of the head andshank.

Another characteristic of the Phillips recess which limits itsusefulness is that, due to its symmetrical design, it is rathersusceptible to the unfavorable effect known as rock-out, that is, thetendency of the driving tool to incline or rock laterally along one orthe other of the crossed groove axes, and thus dislodge itself from therecess, or at least depart sufliciently from its proper coaxialrelationship with the fastener so that difficulty is encountered inproperly driving the fastener, possible damage to the fastener, thework, or both, resulting from this condition. Attempts to develop aPhillips recess of wider and shallower proportions, in order to overcomethe effect noted in the preceding paragraph, have the result ofincreasing the rock-out characteristic of the recess, which thus becomesa limiting factor.

However, the rock-out effect is not limited to screw recesses of thes-o-called Phillips type, but is encountered to a greater or lesserdegree in driving screws having various types of recesses, slots orother tool-engaging means. It is caused by at least two factors which,though always present, have become of increasing importance due to thelarge increase in applied torque which has been employed in recenttimes. The two factors in question are (l) the inevitable loose fit ofdriver and recess, due to manufacturing tolerances and which, also, isto a degree indispensable in order to facilitate entry of the driverinto the recess; and (2) deflection of driver Wings 2,848,024 PatentedAug. 19, 1958 and groove walls. This deflection, which of course has amore pronounced effect on the driver wings than on the groove walls, isa function of applied torque. In earlier times when the screws weredriven by the use of conventional hand screw drivers or power drivers ofrelatively low torque capacity, the said deflection effect was not ofserious proportions. However, with the use of increased applied torqueby means of power drivers, and particularly since it has become thepractice, in many instances, to apply the final tightening effortthrough a torque wrench, deflection of the driver wings has become aserious problem, particularly as it affects the aforesaid rock-outcharacteristic.

The comparatively loose fit of the driver bit in the screw recessaggravates the rock-out problem no matter what the form of the screwrecess and, as mentioned above, such loose fit is inevitable incommercial practice. Moreover, the tendency in screw recess developmenthas been toward shallower and still shallower recesses. Any recess, ifdeep enough, will substantially eliminate the rock-out problem, but itis impractical for various reasons to make and use screws havingrecesses which are deep enough to serve this purpose.

Driver wing deflection takes the form of a spiral deformation of thewings. That is, since the upper edges of the wings are integral with theshank of the driver bit the wing deflection, measured in degrees,increases downwardly toward the tip of the driver bit. The result is aspiral deformation of the wings, causing a reaction the axial componentof which is a force tending to throw the driver out of the recess, andwhich also enhances the rock-out effect.

The torque used in driving recessed-head screws has been increased, inthe last decade, by at least ten times, and characteristics which wereformerly of little or no importance have become critical. One of theseis the rockout characteristic discussed above, and since the finaltightening is now frequently performed by means of the aforesaid torquewrench which applies all of the torque on one side of the screw, givingan unbalanced force on the driver, the danger of rock-out is vastlyincreased.

The torque capacity of the screw and driver combination is also subjectto limitation by reason of the design of the driver tip, which is ofcourse substantially complementary to the screw recess. If the recesshas a sufficiently high torque capacity, the overall capacity of thecombination may depend upon the capacity of the driver, failure of thelatter frequently occurring due to an inadequate strength through thecentral portion of the driver tip, corresponding to the central portionof the screw head recess.

We have recently invented a threaded fastener having a tool-receivingrecess designed to impart a maximum torque capacity to the screw itself,while at the same time eliminating the aforesaid rock-out characteristicand also permitting the use of a stronger driving tool, all of whichfactors result in a substantial increase in the overall torque capacityof the screw and driver combination, and increase its usefulness. Thegeneral object of the present invention is the provision of a drivingtool for use with the new recess, which is more particularly describedin our copending application Serial No. 494,726, filed March 16, 1955.

-Another object is the provision of a driver for threaded fastenershaving tool-engaging recesses with offset grooves, which drivercomprises a shank portion and a bit portion formed on one end thereof,said bit portion comprising a central nib having alternate wings andchannels, said wings extending generally radially but having theirmedial planes offset rearwardly relatively to the direction of drivingrotation, the driving wall of each said wing being disposed closer to atrue radial plane parallel to said medial plane than is the removingwall.

A further object of the invention is the provision of a driving tool ofthe character described, the central nib being of larger diameter and,accordingly, of greater strength than is possible of achievement withdriving tools of the designs heretofore employed, whereby the overalltorque capacity of the screw and driver combination is substantiallyenhanced.

Another object is the provision of a driving tool of the characterdescribed, the substantially radial wings being arranged in angularlyspaced oppositely directed pairs, the wings of each pair being staggeredor displaced with respect to each other so as to eliminate rock-out.

Other and further objects, features and advantages will be apparent fromthe description which follows, read in connection with the accompanyingdrawings in which:

Figure 1 is a fragmentary side elevational view of a driving toolfashioned in accordance with the present invention;

Figure 2 is an end elevation of the tool illustrated in Figure 1;

Figure 3 is an end elevation of a modification of the tool illustratedin Figures 1 and 2, superimposed upon the corresponding outline of aprior art driver (the latter being shown in dotted lines);

Figure 4 is a diagram illustrating an advantage of the present screwdriver form; and

Figure 5 is a view similar to Figure 1 illustrating a furthermodification.

In order to facilitate an understanding of the invention, reference ismade to the embodiments thereof shown in the accompanying drawings anddetailed descriptive language is employed. It will nevertheless beunderstood that no limitation of the invention is thereby intended andthat various changes and alterations are contemplated such as wouldordinarily occur to one skilled in the are to which the inventionrelates.

Referring to Figures 1 and 2, the driving tool there illustratedcomprises a shank portion which may be of any suitable length and may befitted with a handle, for manual use, or may be adapted to be gripped inthe chuck of a power tool. One end of the shank 10 is shaped to form abit portion designated generally by the reference numeral 11 andcomprising a central nib 12 having alternate wings 13 separated bychannels 14, the Wings 13 projecting substantially radially from the nib12. The tip of the latter preferably is formed as a shallow invertedcone, the conical surface 15 extending outwardly to a line 16 on thebottom wall of each wing 13. A second conical surface forms the bottomwall portion 17 of each wing 13, joining the peripheral wall portion 18of the wing along the line 19. As seen in Figure 2, the channels 14 areso formed as to leave fiat wall portions on the adjacent sides ofadjacent wings, the wing wall portion 20 being designated as the drivingwall of the wing, since the wall 20 transmits driving torque to thefastener when the latter is provided with the usual righthand thread.The opposite wing wall 21 is designated as the removing wall of thewing. The wall 20 of each wing is joined to the wall 21 of the adjacentwing by a curved surface 9.

In the embodiment illustrated in Figures 1 and 2, the driving wall 20 ofeach wing 13 lies on a true radial plane, i. e. lies in a plane whichalso contains the longitudinal axis of the driving tool, while theremoving wall 21 is displaced somewhat rearwardly, relative to thedirection of driving rotation of the tool. Preferably, though notessentially, the walls 20 and 21 are parallel to each other and, hence,to the medial plane of the wing, said medial plane being offsetrearwardly relative to the direction of driving rotation. The medialplane, thus, is not a true radial plane but is substantially parallel toa true radial plane, i. e. one containing the longitudinal axis of thedriving tool.

By virtue of the construction thus described, it will be seen that theseveral wings of the driver are offset or staggered in such a mannerthat, when used with a fastener having a complementary recess, therock-out" characteristic is substantially eliminated, the driving toolbeing removable from the recess only in a substantially axial direction.Also, by virtue of the fact that the driving walls 20 lie on or neartruly radial planes, the turning force exerted thereon by the handle orpower tool, as the case may be, is transmitted to the recess walls ofthe fastener in an exactly normal or substantially normal direction, forgreatest efficiency. Thus in Figure 4 it may be seen that a turningforce F applied by the wing surface 26 of a driver of the presentinvention is all useful, while the same force applied to thecorresponding surface of a screw having a symmetrical recess surface bythe surface 27 of a symmetrical driver includes a component F sine onwhich is not only not useful, but is harmful since it tends to deformthe screw recess, the driver Wings, or both. The angle a is the anglebetween the side wall of a groove of a conventional Phillips recess, anda plane containing the screw axis (i. e. a radial plane) and containingthe intersection of said groove side wall with the top of the end wallof the groove. The useful component of the turning force transmittedthrough the screw driver is, of course, that component which is normalto a radial plane of the driver.

The effect just noted may be appreciated from a comparison of therespective outlines shown in Figure 3, in which the dotted outline ofthe bit portion of a conventional Phillips driver is indicated at 22,while the bit portion of a driver constructed in accordance with thepresent invention is seen in solid lines. In the embodiment illustratedin Figure 3, the wings 13 are offset rearwardly, but not to the extentshown in Figures 1 and 2, the driving walls 20 of Figure 3 being closelyadjacent true radial planes, rather than disposed in such planes.Adjacent walls of adjacent wings are connected by two intersecting planesurfaces 23 and 24 rather than by the single curved surface 9 of Figure2.

Figure 3 illustrates how the nib 25 of the driving tool constructed inaccordance with the invention having offset wmgs and largercross-sectional area will have a better section modulus than thecorresponding nib of a conventional Phillips driver, thus enhancing theoverall strength of the driver and of the screw and driver combination.The section modulus may be considered the ratio of the maximumcross-section of the bit to the maximum radius, in this case, thedistance from the center to the furthest point on line 19, Figures 1 and2. It will be recognized that the section modulus is a true measure ofthe torsional strength or deflection and, therefore, the offsetting ofthe Wings has a strengthening effect independent in itself of theincrease in cross-sectional area.

It will be apparent that when the wings 13 or 13' of a driver, accordingto the present invention, are offset rearwardly relative to the drivingdirection, the removing walls 21 or 21 are increased in area, thusfacilitating the use of the tool in the removal of fasteners which havebecome frozen in place. This increase in area of the removing walls ofthe wings, together with the enlargement of the diameter of the nibportion of the driver, considerably enhances the usefulness of thedriver in the removal of such fasteners.

The nib surfaces connecting adjacent walls of adjacent wings may beeither curved or flat, as desired, regardless of the degree of offset ofthe wings themselves. That is, the fiat surfaces 23, 24 of Figure 3 maybe substituted for the curved surfaces 9 of Figure 2, and vice versa.Also, while the wings 13 are preferably arranged in angularly spaced,oppositely directed pairs, an odd 5 number of wings may be employed inspecial cases, if desired.

In some cases it may be desirable, in order to facilitate entry of thedriver into its mating recess, to provide wing walls which convergedownwardly, thus imparting to the wings a slight vertical taper. Thismay be accomplished by providing either or both of the generally radialwing walls with a slight vertical inclination to the driver axis. Thus,in the embodiment illustrated in Figure 5, which otherwise correspondsprecisely with Figure 1, the wall 28 is shown as tapering downwardlytoward the driving wall 20 which, in this embodiment, is preciselyradial.

As employed in the claims hereof, the expression vertical medial planeis intended to signify a plane which is substantially parallel to thelongitudinal axis of the driver and contains (1) the midpoint of a linejoining the intersections of the respective wing walls 20 and 21 withthe outer edge of the bottom wall 17, and (2) the midpoint of a linejoining the intersections of the respective wing walls with the inneredge of the bottom wall.

If the walls 20 and 21 are parallel or have equal and oppositehorizontal and/or vertical tapers, the vertical medial plane of eachwing will be exactly parallel to some radial plane (i. e. a planecontaining the driver axis). If the respective walls 20 and 21 difier invertical taper the vertical medial plane Will have a slight inclinationto the driver axis and thus to any radial plane, while if the walls 20and 21 differ in horizontal taper, but not in vertical taper, thevertical medial plane Will nevertheless be parallel to a true radialplane. In the appended claims, the true radial plane to which the sidewalls of each wing are referred, is that radial plane to which thevertical medial plane is most nearly parallel.

Having thus described the invention, What is claimed as new and desiredto be secured by Letters Patent is:

1. A driver for threaded fasteners having recessed heads, said drivercomprising a shank portion and a shaped bit portion, the bit portionproviding a central nib and a plurality of wings extending outwardlytherefrom, said nib projecting axially beyond said wings, said wingsextending generally radially and with equal angularities of less than180 between adjacent wings, and having their vertical medial planessubstantially parallel to, but displaced from, true radial planes, thedriving Wall of each said wing lying closer to said respectivesubstantially parallel true radial plane than does the opposite wall ofthe same wing.

2. A driver as defined in claim 1, said driving walls lying in planesparallel to said true radial planes.

3. A driver as defined in claim 1, said wing Walls lying in planesparallel to said true radial planes.

4. A driver as defined in claim 1, said driving walls lying in saidradial planes.

5. A driver as defined in claim 1, said wings being arranged in equallyangularly spaced, oppositely directed palrs.

6. A driver as defined in claim 5, saidwings being four in number.

7. A driver as defined in claim 1, said driving and opposite walls ofeach wing lying in planes differing slightly in angular relation to thedriver axis, said vertical medial planes being slightly inclined to saidaxis.

8. A driver as defined in claim 7, said driving walls lying in planesparallel to said axis.

References Cited in the file of this patent UNITED STATES PATENTS789,274 Hamlon May 9, 1905 1,080,707 Mackie et a1. Dec. 9, 19131,758,945 Grube May 20, 1930 1,844,241 Bryant Feb. 9, 1932 2,046,837Phillips July 7, 1936 2,601,453 Phipard June 24, 1952 FOREIGN PATENTS7,741 Germany Oct. 17, 1879

